ImageTagTest tries to assert that uppercase tags cannot be added to docker images. But it has 2 flaws:

• it tries to assert the existence of an error dialog (when providing an uppercase tag) via

  new ShellWithTextIsAvailable("Error tagging image to <" + imageTagUppercase + ">")

  but ShellWithTextIsAvailable is an AbstractWaitCondition. So it has no effect at all

• the docker tooling wont prevent you from providing an uppercase tag. It will actually accept it, send it to the daemon and then display it. No error occurrs. See https://bugs.eclipse.org/bugs/show_bug.cgi?id=509223

The assertion itself is absolutely correct. The cmd line wont accept uppercase letters in a tag.